For example, in a factory line, in order to cooperatively operate a plurality of node apparatuses, it is required that each node apparatus has a common time with which operation timing is regulated.
A network connects node apparatuses, and a mechanism for making each node apparatus to have the common time via the network is known as time synchronization.
Time synchronization between node apparatuses is performed between a node apparatus (hereinafter referred to as a master apparatus) having a reference time and node apparatus (hereinafter referred to as a slave apparatus) that makes an internal time coincide with the reference time.
Usually, time synchronization is operated by the following procedure.
(1) The master apparatus computes a propagation delay (calculation value) to each slave apparatus and notifies each slave apparatus of the propagation delay.
(2) The master apparatus transmits a synchronous frame in which a transmission time is held to the slave apparatus.
(3) The slave apparatus sets a reception time of the synchronous frame to a synchronous time {transmission time+propagation delay (calculation value)}.
However, since a propagation delay (actual measurement value) taken from the above (2) to (3) varies, a deviation occurred between the propagation delay (calculation value) computed in (1) and the propagation delay (actual measurement value) causes a synchronous error.
In a conventional time synchronization, based on a stochastic process, the slave apparatus restrains the synchronous error by measuring the transition of the propagation delay (actual measurement value) and estimating the propagation delay (actual measurement value) (for example, Patent Literature 1).